1. Technical Field of the Invention
The present invention relates generally to the field of hotmix asphalt concrete and asphalt technology. More specifically, the present invention relates to the pretreatment or priming of aggregate for use with asphalt or other petroleum-derived binders.
2. Description of the Related Art
The current practice to produce hotmix asphalt concrete is to heat up aggregate either in a continuous drum or batch hotmix asphalt concrete plant and spray asphalt binder onto the very hot aggregate. The combination of these two components is an asphalt binder-aggregate product used to create pavement. The asphalt binder provides flexibility to the resulting asphalt binder-aggregate product and is therefore used to ease the constructability of pavements. However, a drawback to the asphalt-aggregate product is that adhesion strength of the binder to the aggregate is comparatively low and the binder is essentially a high viscosity fluid, as opposed to a solid at room temperature, such that the asphalt binder-aggregate interface created by mixing the two represents a weak-spot where failure can occur. In particular, water, which is very polar, can penetrate the product and separate the binder from the aggregate. This is generally caused by either freeze-thaw cycles or via pump action of the water in the voids during traffic loading. Once the adhesion between the binder and the aggregate is lost the pavement can unravel. Commonly used tests to evaluate the susceptibility of mixes to water damage are the modified Lotman test (AASHTO T283) and the Hamburg Wheel Tracking (HWT) Test, as understood by those of skill in the art. To meet the test specification requirements, it is known to use lime, hydrated lime or lime marination of the aggregate. It is also known to add a liquid amine antistripping agent to the asphalt binder.
Efforts to overcome low temperature and fatigue cracking issues have led to the development of the products noted above which in turn suffer from rutting and shoving over periods of use. It is possible to improve the rut resistance with conventional and polymer-modified asphalts; however, this is generally accomplished by sacrificing the low temperature binder properties. Polymer modification does not, generally, improve the intermediate temperature properties. Furthermore, polymer addition accounts for a significant increase in cost. It is desirable to develop a product and process to create the product that overcomes low temperature and fatigue cracking issues while resisting rutting and shoving with use.
Attempts have been made to improve interfacial properties in asphalt mixtures to increase performance. For example, U.S. Pat. No. 5,223,031 by Sugi et al. titled “Cement/Asphalt Mixtures and Processed for Preparation of the Same” provides a cement/asphalt mixture comprising an aggregate, an asphalt emulsion, cement, a hydraulic inorganic material and water, characterized in that the surfaces of aggregate fragments are covered with the asphalt particles prepared by the coalescence of asphalt emulsion and that the hydraulic inorganic material and water are present in the interstices between the aggregate fragments. The cement/asphalt mixtures is prepared through a process characterized by the steps of adding a cationic or anionic asphalt emulsion to an aggregate and mixing the two by stirring with a mixer for about 10 to 60 seconds. Afterwards, the resulting mixture is further mixed with a hydraulic inorganic material to produce the cement/asphalt mixture. During the process, the aggregate can be heated to a temperature of lower than 120 deg. C. (i.e., lower than 248 deg. F.) to accelerate the coalescence of asphalt emulsion when the operation is conducted in a cold environment.
In Europe, in particular, contractors and refiners have promoted the use of ultra-high modulus binders to reduce traffic-induced deformation. Because of the moderate climate in most of South-central Europe, the reduction in low temperature performance has not been a cause of concern. However, in the United States, Northern Europe, as well as Eastern Europe, the climatic conditions are much more severe and have led to disadvantages. Because of their propensity to exhibit severe cracking, refined low-penetration ultra-high modulus mixes are generally unacceptable in these climates. Hence, there is a need for a modification to hotmix asphalt concrete mixes that would increase the resistance to permanent deformation and increase the modulus of the mix at intermediate temperatures without affecting the binder properties significantly. A further need exists for improved interfacial properties in asphalt mixtures, particularly for use in low temperature climates. It would also be desirable if these improvements could be accomplished while improving the interfacial properties of the asphalt aggregate interface, which in turn enhances the moisture resistance of the hotmix asphalt.